7.28 Comment syntax

The MySQL server supports the # to end of line, -- to end of line and /* in-line or multiple-line */ comment styles:

mysql> select 1+1;     # This comment continues to the end of line
mysql> select 1+1;     -- This comment continues to the end of line 
mysql> select 1 /* this is an in-line comment */ + 1;
mysql> select 1+
/*
this is a
multiple-line comment
*/
1;

Note that the -- comment style requires you to have at least one space after the --!

Although the server understands the comment syntax just described, there are some limitations on the way that the mysql client parses /* ... */ comments:

• Single-quote and double-quote characters are taken to indicate the beginning of a quoted string, even within a comment. If the quote is not matched by a second quote within the comment, the parser doesn't realize the comment has ended. If you are running mysql interactively, you can tell that it has gotten confused like this because the prompt changes from mysql> to '> or ">.
• A semicolon is taken to indicate the end of the current SQL statement and anything following it to indicate the beginning of the next statement.

These limitations apply both when you run mysql interactively and when you put commands in a file and tell mysql to read its input from that file with mysql < some-file.

MySQL doesn't support the `--' ANSI SQL comment style. 5.3.7 `--' as the start of a comment.